This invention relates to a drawer interlock system for a multi-drawer article of furniture such as a filing cabinet.
Drawer interlock systems are intended to prevent more than one drawer of a filing cabinet being opened at the same time, to guard against the cabinet tipping over.
U.S. Pat. No. 4,480,883 (Young) discloses an example of a prior art interlock mechanism which is designed on the principle that there is free space or xe2x80x9cplayxe2x80x9d in the mechanism which is taken up when one drawer is opened, so that no other drawer can be opened. In the mechanism disclosed in the Young patent, a series of locking bars and intervening cam elements are stacked in a vertical channel at one side of the drawers of an upright filing cabinet. When one drawer is opened, the cam element associated with that drawer is turned, which vertically displaces the locking bars and takes up all of the available free space in the channel. The cam elements associated with the other drawers then cannot be turned and are effectively xe2x80x9clocked outxe2x80x9d.
A difficulty with some prior art interlock systems is that they have a tendency to jam. For example, the cam element disclosed in the Young patent is rectangular in section and is disposed between adjacent locking bars for turning through 90xc2x0 between a position in which the wide faces of the member are horizontal to a position in which the wide faces are vertical, spreading apart the locking bars. There is significant potential for jamming of the corners of the cam element against end faces of the respective locking bars.
A further disadvantage is that significant lateral forces are imposed on the interlock mechanism when a drawer is opened. Not only does this tend to make the mechanism noisy, but it is possible for the cam elements to over-rotate, leading to damage or jamming of the mechanism.
Examples of other prior art U.S. patents dealing with interlock systems are as follows:
An object of the present invention is to provide a drawer interlock system that addresses the disadvantages of the prior art.
The system provided by the invention is intended for use with a furniture article such as a filing cabinet, that includes a cabinet structure and at least two drawers, each of which is supported in the cabinet for movement between an open position and a closed position with respect to the cabinet. The system includes, in association with each drawer, a cam unit that is mounted on the cabinet and that includes a rotary cam assembly extending about an axis normal to the direction of movement of the associated drawer between its open and closed positions. The respective cam units are aligned on the said axis. Each cam assembly includes a rotary cam and a stationary (i.e. non-rotary) cam. The rotary cam is turnable about the said axis in response to movement in the associated drawer, between the normal position when the drawer is closed and an interlock actuating position when the drawer is open. The respective cams have co-operating cam surfaces shaped to cause (1) displacement of the stationary cam a pre-determined distance outwardly along said axis in response to turning of the rotary cam from its normal position to its interlock actuating position and (2) locking of the cams with respect to one another in the event that said displacement of the secondary cam is prevented. A locking element extends between the cam units and connects the stationary cams of the respective units. The locking element is axially displaceable in response to displacement of the stationary cam through said pre-determined distance. The system also includes means limiting axial displacement of the locking element to the pre-determined distance, so that the rotary cam of only one cam unit at a time can move to the interlock actuating position, whereupon the rotary cam of the other cam unit is locked in the normal position. The rotary cam is designed to then prevent opening of the drawer associated with that cam.
The interlock system of the invention is based generally on the same principle as prior art interlock systems discussed previously, in which there is a limited amount of free movement that is taken up when one drawer is opened, so that the system is then locked and no other drawer can be opened. However, an important distinction of the invention is that the system includes rotary cam units that incorporate in-line cams disposed on a common axis. Only minimum lateral forces are imposed on the interlock system when a particular drawer is opened and those forces are translated by the rotary cam assembly into axial forces that result in locking of the system. As such, the potential for damage to the interlock system is reduced as compared with the prior art and the system can be designed to operate much more smoothly and more quietly than prior art systems.
Preferably, the cams of the various cam units are plastic mouldings, so that there is essentially no noise when the cams operate. The cam surfaces may comprise a pair of diametrally spaced lobes and intervening recesses on one cam, and complimentary lobes and recesses on the co-operating cam. The lobes can be appropriately contoured to achieve the required cam effects, with minimum noise.
The interlock system of the invention has been designed primarily for use in association with a vertical file cabinet, in which case the interlock system extends vertically inside the cabinet adjacent one side of the drawer opening. In principle, however, the interlock system could also be used for a horizontal file cabinet by positioning the system generally horizontally, either above or below the drawer opening in the cabinet, and providing appropriate actuator elements on the drawers.
As indicated previously, the interlock system will include a cam unit for each drawer and the cam units will be interconnected by locking elements (typically rods). Accordingly, the number of rods will be one less than the number of cam units. In an example of a vertical file cabinet having three drawers, there will be one cam unit associated with each drawer and two rods, one extending up from the lower cam unit to the centre cam unit and the other extending up from that cam unit to the top cam unit. The centre cam unit will have two stationary cams, one co-operating with the lower rod and the other co-operating with the upper rod. The top cam unit may incorporate the required means for limiting axial displacement of the locking elements.